INTERRUPT. OF PCM/BCM WHEN DIAG. TOOL IS CONNECTED

SUBJECT: INTERRUP. OF PCM-BCM COMMUNICATION WHEN DIAGNOSTIC TOOL IS CONNECTED TO THE SERIAL DATA- ALDL (NEW REV. MEMCAL)

VEHICLES AFFECTED: 91 E CAR

Breakpoints are as follows: Riviera Federal Calib. MU409849 Calif. Calib. MU409802 Reatta Federal Calib. MB900565 Calif. Calib. MB900548 Toronado Federal Calib. MU306201 Calif. Calib. MU306180

Some 1991 E models equipped with 3800 T.P.I. (VIN L) engine, built prior to VINS listed, may have a condition that prevents the PCM from communicating with the BCM when a diagnostic tool is connected to the vehicle's serial data (ALDL) connector. This condition only occurs when a diagnostic tool is connected to the vehicle's ALDL connector.

Should this condition exist on a vehicle, technicians may observe specific functions that are affected.

o A/C clutch remains on or off o BCM Code 334 (BCM-PCM communication error) is stored o Coolant temperature gauge and tachometer are not displayed

This condition may lead to improper diagnosis and unnecessary repairs. It is recommended that a new revised calibration mem-cal be installed.

Scanner I.D. Model Axle With This Broadcast Service Year Application Ratio Memcal Installed Code Part ---- --------------- ------- ------------- ------- -------- 1991 Riviera/Toronado 3.06 Fed. 1464 AXMU 16162582 1991 Riviera/Toronado 3.06 Calif. 1474 AXMW 16162586 1991 Reatta 3.33 Fed. 1484 AXMX 16162590 1991 Reatta 3.33 Calif. 1494 AXMY 16162594

Use the most applicable Labour Operation and Time from the Canadian Labour Time Guide.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.